Jeff and Craig, thank you for answering my question.
@Craig: The suggestion of using a report is not possible, I am sorry.
I made a report function in my Delphi program, in which I can place a Sql-instruction.
When they push a button it produces an Excel result.
@Jeff: The quirky update solution is to difficult for this use, I am sorry again.
The user wants a list of the amount of bookings per week.
I use the excellent isoweek solution of Jeff (I am so happy with this publication).
There are not so much bookings in a year (a max of 5000), and after a year al bookings are written to a history file and it starts again from zero.
A simple COUNT(*) and a GROUP BY IsoWeek, gives the user the most recent bookings per week.
Knowing that adding a running total is difficult, I'll only add a grand total, that's what the user gets.
Thank you for your effort